Copolyester having gas-barrier property

ABSTRACT

A copolyester having an intrinsic viscosity, measured in o-chlorophenol at 25° C., of 0.3 to 1.5 dl/g and being derived from dicarboxylic acid units composed of 95 to 60 mole % of isophthalic acid units and 5 to 40 mole % of 2,6-naphthalenedicarboxylic acid units and dihydroxy compound units composed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole % of 1,3-bis(2-hydroxyethoxy)benzene units; a gas barrier imparting agent composed of the copolyester; a polyester composition composed of (A) a polyethylene terephthlate and (B) the copolyester; and a film, a preform and a container composed of the polyester composition. Also provided are a polyester laminated structure, a stretched laminated structure, a preform and a laminated blow-molded article each composed of (C) a polyalkylene terephthalate layer and (D) a copolyester layer composed of the copolyester or the polyester composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a copolyester and a gas-barrier propertyimparting agent, and more specifically, to a copolyester havingexcellent gas-barrier property and surface properties and a high glasstransition temperature and a gas-barrier property imparting agentcomposed of the copolyester.

The invention also relates to a polyester composition and a film, apreform and a container composed of the polyester composition, and morespecifically, to a polyester composition having excellent gas-barrierproperty, surface properties and transparency and comprising (A)polyethylene terephthalate and (B) the aforesaid copolyester, and to afilm, a preform and a container composed of the polyester composition.

Furthermore, this invention relates to a polyester laminated structure,and its use, and more specifically, to a polyester laminated structurehaving excellent moldability, mechanical properties and composed of (C)a polyalkylene terephthalate layer and (D) a copolyester layer composedof the aforesaid copolyester or a polyester composition, and to its use.

2. Description of the Prior Art

Glass has widely been used as a material for containers for holdingvarious articles, for example seasonings, oils, wines and liquors, beer,soft drinks including carbonated drinks, cosmetics, and detergents.Glass containers have excellent gas-barrier property, but their cost ofproduction is high. It is the usual practice therefore to recover theused empty containers and recycle them for use. The glass containers,however, are heavy and involve high transportation expenses. Moreover,they are susceptible to breakage and inconvenient to handle.

To solve this problem, the glass containers have been superseded byvarious plastic containers, and various plastic materials are usedaccording to the kind of articles to be held and the purpose of use.Polyethylene terephthalate (PET) has excellent thermal resistance,impact strength, gas-barrier property and transparency, and is used as amaterial for containers used to hold seasonings, refreshing drinks,detergents and cosmetics. In the case of containers for beer andcarbonated drinks which most rigorously require gas-barrier property,polyethylene terephthalate is still not entirely satisfactory. To usepolyethylene terephthalate for such containers, it is necessary toimprove gas-barrier property by increasing the thickness of thecontainers.

Polyester containers have shown an increasing demand, but to expandtheir use further, it is strongly desired to develop polyesters havingexcellent gas-barrier property and melt-moldability.

Japanese Laid-Open Patent Publication No. 84866/1981 discloses amultilayer container having a thin wall portion in which the outermostlayer and the innermost layer are composed of a polyester havingethylene terephthalate as main recurring units, an interlayer iscomposed of a polyamide obtained by reacting a dibasic acid componentand a diamine component, the diamine component being m-xylylenediamineor a mixture of it with p-xylylenediamine, and the resin constitutingthe thin wall portion is oriented in at least one direction. This patentdocument describes that the above container has excellent oxygengas-barrier property while retaining the excellent dynamical properties,transparency and chemical resistance of the polyester.

Japanese Laid-Open Patent Publication No. 183248/1983 discloses abiaxially stretched blow molded bottle in which both inside and outsidesurface layers are composed of polyethylene terephthalate and a layerintermediate between them is composed of a mixture of polyethyleneterephthalate and a xylylene group-containing polyamide.

Japanese Laid-Open Patent Publication No. 64624/1984 discloses apolyalkylene isophthalate such as polyethylene isophthalate and itscopolymer, and a packaging material having good gas-barrier propertywith respect to oxygen and carbon dioxide gas which is molded from them.

Japanese Laid-Open Patent Publication No. 87049/1984 discloses amultilayer packaging material composed of a layer of a polyalkyleneisophthalate or its copolymer and a layer of a polyalkyleneterephthalate such as polyethylene terephthalate or its copolymer, and amolded article such as a bottle formed from it.

Japanese Laid-Open Patent Publication No. 64658/1984 proposes a methodof blending polyethylene isophthalate and polyethylene terephthalate.

However, the polyethylene isophthalates described in the above-citedpatent documents contains high-melting oligomers, and these oligomersadversely affect the physical properties of the resulting moldedarticles.

To improve the gas-barrier property of PET, a copolyester was proposedwhich is prepared by copolymerizing isophthalic acid as a dicarboxylicacid component and ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzeneas a dihydroxy compound component (see Japanese Laid-Open PatentPublication No. 167617/1983).

If an article such as a container is molded from a polyester resincontaining moisture, hydrolysis takes place and the mechanicalproperties of the molded article are degraded. It is necessary thereforeto dry the polyester resin before molding. However, since anisophthalate-type copolyester containing a large amount of isophthalicacid as the dicarboxylic acid component has a lower crystallinity andglass transition temperature (Tg) than a terephthalate-type copolyester,it can be dried only at low temperatures. Accordingly, to obtain anisophthalate-type polyester having a low water content, long periods oftime are required for its drying. If the isophthalate copolyester isdried at temperatures higher than the glass transition temperature, thecopolyester will melt-adhere to itself.

Usually, polyethylene terephthalate is dried at a temperature of 110° C.to 160° C. If the polyethylene terephthalate dried at the abovetemperatures and the isophthalate-type copolyester dried at lowertemperatures are dry-blended immediately after drying, theisophthalate-type copolyester will be heated to a temperature higherthan the glass transition temperature by the polyethylene terephthalatewhich is still at a considerably high resin temperature. Consequently,the pelletized isophthalate-type copolyester will get out of shape orthe copolyester pellets melt-adhere to one another. Consequently, it isdifficult to mix them uniformly.

For this reason, it has been desired to develop an isophthalate-typecopolyester having a high glass transition temperature (Tg) andexcellent thermal resistance.

An isophthalate-type copolyester having copolymerized thereinbis(4-beta-hydroxyethoxyphenyl)sulfone was proposed as a copolyesterhaving a high glass transition temperature (Tg) (see Japanese Laid-OpenPatent Publication No. 167617/1983).

The use of bis(4-beta-hydroxyethoxyphenyl)sulfone makes theisophthalate-type copolyester slightly higher in glass transitiontemperature (Tg), but its Tg elevating effect is not sufficient. Inaddition, if its gas-barrier property is degraded, or the copolyester iscolored or the monomeric components bleed out, the polyester isundesirable in view of food sanitation.

SUMMARY OF THE INVENTION

It is an object of this invention to solve the above problems in theprior art, and to provide an isophthalate-type copolyester being freefrom high-melting oligomers and having a high glass transitiontemperature and excellent gas-barrier property and surface properties.

Another object of this invention is to provide a gas-barrier propertyimparting agent comprising the above isophthalate-type copolyester.Another object of this invention is to solve the problems associatedwith the prior art discussed above, and to provide a polyestercomposition which does not contain high-melting oligomers, can be driedat a high speed and has excellent thermal resistance, impact strength,surface properties, transparency and gas-barrier properties.

Another object of this invention is to provide a film, a preform and acontainer composed of the above polyester composition.

Another object of this invention is to solve the problems associatedwith the prior art discussed above, and to provide a polyester laminatedstructure which is free from high-melting oligomers, and has excellentmoldability, stretchability, gas-barrier property, especially withrespect to oxygen and carbon dioxide gas, thermal resistance, impactstrength, surface properties, transparency, electrical properties andchemical resistance.

Another object of this invention is to provide a stretched laminatedstructure, a preform for blow molding and a laminated blow-moldedarticle each composed of the above polyester laminated structure andhaving excellent gas-barrier property, especially with respect to oxygenand carbon dioxide gas, thermal resistance, impact strength, surfaceproperties, transparency, electrical properties and chemical resistance.

The above objects are achieved in accordance with this invention by acopolyester having an intrinsic viscosity, measured in o-chlorophenol at25° C., of 0.3 to 1.5 dl/g and being derived from dicarboxylic acidunits composed of 95 to 60 mole % of isophthalic acid units and 5 to 40mole % of 2,6-naphthalenedicarboxylic acid units and dihydroxy compoundunits composed of 95 to 70 mole % of ethylene glycol units and 5 to 30mole % of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are also achieved in accordance with this invention bya gas-barrier property imparting agent composed of a copolyester havingan intrinsic viscosity, measured in o-chlorophenol at 25° C., of 0.3 to1.5 dl/g and being derived from a dicarboxylic acid units composed of 95to 60 mole % of isophthalic acid units and 5 to 40 mole % of2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are further achieved in accordance with this inventionby a polyester composition comprising (A) 50% to 95% by weight ofpolyethylene terephthalate and (B) 50% to 5% by weight of a copolyesterhaving an intrinsic viscosity, measured in o-chlorophenol at 25° C., of0.3 to 1.5 dl/g and being derived from dicarboxylic acid units composedof 95 to 60 mole % of isophthalic acid units and 5 to 40 mole % of2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are further achieved in accordance with this inventionby a film composed of a polyester composition comprising (A) 50% to 95%by weight of polyethylene terephthalate and (B) 50% to 5% by weight of acopolyester having an intrinsic viscosity, measured in o-chlorophenol at25° C., of 0.3 to 1.5 dl/g and being derived from dicarboxylic acidunits composed of 95 to 60 mole % of isophthalic acid units and 5 to 40mole % of 2,6-naphthalenedicarboxylic acid units and dihydroxy compoundunits composed of 95 to 70 mole % of ethylene glycol units and 5 to 30mole % of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are further achieved in accordance with this inventionby a preform composed of a polyester composition comprising (A) 50% to95% by weight of polyethylene terephthalate and (B) 50% to 5% by weightof a copolyester having an intrinsic viscosity, measured ino-chlorophenol at 25° C., of 0.3 to 1.5 dl/g and being derived fromdicarboxylic acid units composed of 95 to 60 mole % of isophthalic acidunits and 5 to 40 mole % of 2,6-naphthalenedicarboxylic acid units anddihydroxy compound units composed of 95 to 70 mole % of ethylene glycolunits and 5 to 30 mole % of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are further achieved in accordance with this inventionby a container composed of a polyester composition comprising (A) 50% to95% by weight of polyethylene terephthalate and (B) 50% to 5% by weightof a copolyester having an intrinsic viscosity, measured ino-chlorophenol at 25° C., of 0.3 to 1.5 dl/g and being derived fromdicarboxylic acid units composed of 95 to 60 mole % of isophthalic acidunits and 5 to 40 mole % of 2,6-naphthalenedicarboxylic acid units anddihydroxy compound units composed of 95 to 70 mole % of ethylene glycolunits and 5 to 30 mole % of 1,3-bis(2-hydroxyethoxy)benzene units.

The above objects are also achieved in accordance with this invention bya polyester laminated structure composed of (C) a polyalkyleneterephthalate layer and (D) a copolyester layer, the copolyester layer(D) derived from dicarboxylic acid units composed of 95 to 60 mole % ofisophthalic acid units and 5 to 40 mole % of 2,6-naphthalenedicarboxylicacid units and dihydroxy compound units composed of 95 to 70 mole % ofethylene glycol units and 5 to 30 mole % of1,3-bis(2-hydroxyethoxy)benzene units, or a copolyester compositioncomprising said copolyester and polyethylene terephthalate.

The above objects are further achieved in accordance with this inventionby a stretched polyester laminated structure composed of (C) apolyalkylene terephthalate layer and (D) a copolyester layer composed ofa copolyester derived from dicarboxylic acid units composed of 95 to 60mole % of isophthalic acid units and 5 to 40 mole % of2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2-hydroxyethoxy)benzene units or a copolyester compositioncomprising said copolyester and polyethylene terephthalate, saidpolyalkylene terephthalate layer (C) and the copolyester layer (D) beingstretched.

The above objects are also achieved in accordance with this invention bya preform for a laminated blow-molded article, said preform composed of(C) a polyalkylene terephthalate layer and (D) a copolyester layer, thecopolyester layer (D) being composed of a copolyester derived fromdicarboxylic acid units composed of 95 to 60 mole % of isophthalic acidunits and 5 to 40 mole % of 2,6-naphthalenedicarboxylic acid units anddihydroxy compound units composed of 95 to 70 mole % of ethylene glycolunits and 5 to 30 mole % of 1,3-bis(2-hydroxyethoxy)benzene units, or acopolyester composition comprising said copolyester and polyethyleneterephthalate.

The above objects are also achieved in accordance with this invention bya polyester laminated blow-molded article composed of (C) a polyalkyleneterephthalate layer and (D) a copolyester layer, the copolyester layer(D) being composed of a copolyester derived from dicarboxylic acid unitscomposed of 95 to 60 mole % of isophthalic acid units and 5 to 40 mole %of 2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2-hydroxyethoxy)benzene units, or a copolyester compositioncomprising said copolyester and polyethylene terephthalate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The copolyester of this invention is characterized in that thedicarboxylic acid units (recurring units derived from a dicarboxylicacid) consist of 95 to 60 mole % of isophthalic acid units and 5 to 40mole % of 2,6-naphthalenedicarboxylic acid units and the dihydroxycompound units (recurring units derived from a dihydroxy compound)consist of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2-hydroxyethoxy)benzene units, and that it has an intrinsicviscosity, measured in o-chlorophenol at 25° C., of 0.3 to 1.5 dl/g.

Since the copolyester of the invention uses isophthalic acid units and2,6-naphthalenedicarboxylic acid units as the dicarboxylic acid unitsand ethylene glycol units and 1,3-bis(2-hydroxyethoxy)benzene units asthe dihydroxy compound units, it does not contain high-melting oligomersand has excellent gas-barrier property and surface properties and a highglass transition temperature.

The copolyester of this invention will be described below specifically.

The copolyester of the invention can be obtained by co-condensationreaction of the following dicarboxylic acids and dihydroxy compounds.

The dicarboxylic acids used in this invention are 95 to 60 mole %,preferably 90 to 70 mole %, of isophthalic acid, and 5 to 40 mole %,preferably 10 to 30 mole %, of 2,6-naphthalenedicarboxylic acid.

If the isophthalic acid is used in an amount of more than 95 mole %, theresulting copolyester does not have so high a glass transitiontemperature. If it is used in an amount of less than 60 mole %, theglass transition temperature of the resulting copolyester has too high aglass transition temperature, and a blend of the resulting copolyesterand polyethylene terephthalate, or a multilayer laminate of thecopolyester cannot be sufficiently stretched.

In the present invention, another dicarboxylic acid may be used inaddition to the isophthalic acid and 2,6-naphthalenedicarboxylic acid inan amount which does not impair the properties of the resultingcopolyester. Examples of the other dicarboxylic acid are terephthalicacid, phthalic acid, and 2-methylterephthalic acid. As the dihydroxycompounds, ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene are usedin the invention. These dihydroxy compounds are used in such amountsthat the hydroxy compound component consists of 95 to 70 mole %,preferably 90 to 80 mole %, of ethylene glycol, and 5 to 30 mole %,preferably 10 to 20 mole %, of 1,3-bis(2-hydroxyethoxy)benzene. By usingethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene in the above amountsas the dihydroxy compounds, a copolyester being free from high-meltingoligomers and having excellent surface properties and a high glasstransition temperature can be obtained.

In addition to ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene,another dihydroxy compounds may be used in an amount which does notimpair the properties of the resulting copolyester. Examples of theother dihydroxy compound include dihydroxy compounds having 3 to 15carbon atoms such as 1,3-propanediol, 1,4-butanediol, neopentyl glycol,cyclohexanediol, cyclohexanedimethanol, 1,4-bis(2-hydroxyethoxy)benzene,2,2-bis(4-beta-hydroxyethoxyphenyl)propane andbis(4-beta-hydroxyethoxyphenyl)sulfone.

The copolyester of the invention may be composed only of the abovedicarboxylic acid units and the above dihydroxy compound units, or ofthe dicarboxylic acid units, the hydroxy compound units and a smallamount of trifunctional or higher polycarboxylic acid units orpolyhydroxy compound units. Polycarboxylic acids having 4 to 15 carbonatoms may be used as the trifunctional or higher polycarboxylic acid.Specific examples may be trimellitic acid, trimesic acid andhemimellitic acid. The trifunctional or higher polyhydroxy compounds maybe, for example, polyhydric alcohols having 3 to 15 carbon atoms.Typical examples include 1,1,1-tri(hydroxymethyl)propane, glycerol,1,2,3-butanetriol, 1,2,3-pentanetriol, and pentaerythritol. Polyestersobtained by co-condensing the trifunctional or higher polycarboxylicacid or polyhydroxy compound with the above dicarboxylic acid anddihydroxy compound are preferred because they have improved uniformstretchability in blow molding.

The proportion of the trifunctional or higher polycarboxylic acid unitsin the copolyester is 0.01 to 2 moles, preferably 0.005 to 1 mole, per100 moles of the dicarboxylic acid units, and the proportion of thetrifunctional or higher polyhydroxy compound units is 0.01 to 2 moles,preferably 0.05 to 1 mole, per 100 moles of the drihydroxy compoundunits.

The resulting copolyester of the invention has an intrinsic viscosity,measured in o-chlorophenol at 25° C., of 0.3 to 1.5 dl/g, preferably 0.6to 1.0 dl/g. If the intrinsic viscosity is less than 0.3 dl/g, themechanical strength of the copolyester is undesirably degraded. On theother hand, if it exceeds 1.5 dl/g, the copolyester undesirably hasdegraded melt-moldability.

The copolyester of the invention can be produced by knownpolycondensation reactions heretofore employed in the production ofpolyethylene terephthalate. The dicarboxylic acids may be fed to thereaction system as such or their dialkyl esters. They may also be fed asesters of the dicarboxylic acid with a diol such asbis(beta-hydroxyethyl) alcohol.

Likewise, the dihydroxy compounds may be fed as such or in the form ofdihydroxy esters of the carboxylic acids.

Known catalysts used in the production of polyethylene terephthalate maybe used in the copolycondensation. The catalysts may be, for example,metals such as antimony, germanium and titanium, or their compounds suchas the oxides, hydroxides, halides, inorganic acid salts, organic acidsalts, complex salts, double salts, alcoholates and phenolates. Thesecatalysts may be used singly or in combination with each other. Thecatalyst may be supplied to the reaction system at the initial stage ofthe esterification reaction or ester interchange reaction, or may besupplied to the reaction system before it is switched to thepolycondensation reaction stage.

At the time of the cocondensation, there may be used catalysts forester-interchange reaction, and additives such as inhibitors againstformation of diethylene glycol, heat stabilizers, light stabilizers,lubricants, pigments and dyes, which are used in the production ofpolyethylene terephthalate. Amines such as triethylamine andtri-n-butylamine and quaternary ammonium compounds such as tetraethylammonium hydroxide and tetrabutyl ammonium hydroxide may be used as theinhibitors against the formation of diethylene glycol. Examples of thestabilizers such as heat stabilizers are phosphorus compounds such asphosphoric acid, phosphorous acid, hypophosphoric acid and esters ofthese.

The copolyester of this invention may be produced by a known meltpolycondensation method or at times by using a solid-phasepolycondensation method after the melt polycondensation method.

In the above melt polycondensation, the so-called directpolycondensation or the so-called esterinterchange polycondensation maybe used.

The melt polycondensation method will be described further morespecifically. For example, isophthalic acid and2,6-naphthalenedicarboxylic acid or dicarboxylic acids containing theseas main ingredients and ethylene glycol and1,3-bis(2-hydroxyethoxy)benzene or a condensate thereof with adicarboxylic acid, and optionally a trifunctional or higher compoundcontaining at least three carboxyl or hydroxyl groups are esterified orester-interchanged simultaneously or consecutively at a temperature ofpreferably 100° C. to 280° C., and then polycondensing the resultingpre-polycondensate at a temperature above its melting point, preferably200° C. to 300° C. under vacuum or in the presence of a flowing inertgas with stirring.

Furthermore, the copolyester of the invention may be produced bysubjecting the copolyester obtained by the above melt polycondensationmethod to solid-phase polycondensation method to increase its molecularweights. Specifically, this solid-phase polycondensation method iscarried out by pelletizing the copolyester obtained by the meltpolycondensation method and maintaining the pellets at a temperaturebelow the melting point, preferably 180° C. to 240° C., under vacuum orin a stream of an inert gas.

The copolyester of this invention has a higher glass transitiontemperature than a polyester obtained from isophthalic acid and ethyleneglycol, and can be dried more rapidly. Furthermore, the copolyester ofthis invention has better gas-barrier property than a polyester obtainedfrom terephthalic acid and ethylene glycol. The copolyester of theinvention hardly contains high-melting oligomers, and can give a moldedarticle having excellent surface properties.

The copolyester of the invention can be used as a gas-barrier impartingagent because it has excellent gas-barrier property and surface propertyand a high glass transition temperature.

The copolyester of the invention may, as required, contain othercomponents such as coloring agents, fillers, polymerization catalysts,and crosslinking agents such as trimellitic anhydride, trimesic acid ortriols.

The copolyester of the invention may be used in the unstretched state asa material for articles of various shapes such as films, sheets, fibersand containers to be obtained by ordinary molding methods. When thecopolyester in the stretched state is molded into films, sheets andcontainers, these articles have further improved gas-barrier property.

Since the copolyester of the invention has excellent gas-barrierproperty, it can be used as a packaging material such as a bottle byusing it as a single layer or as a laminate with another layer such as alayer of polyethylene terephthalate, nylon 6 or nylon 66.

Furthermore, a packaging material having excellent gas-barrier propertycan be prepared by blending the copolyester of the invention withanother polyester such as polyethylene terephthalate.

Now, a stretched product of the copolyester of the invention will bedescribed. This stretched product is monoaxially or biaxially stretchedand may be in the form of a film, a sheet, a fiber, or a blow-moldedcontainer. Where the copolyester is monoaxially stretched, the stretchratio is usually from 1.1 to 10, preferably from 1.2 to 8, especiallypreferably from 1.5 to 7. Where the copolyester is stretched biaxially,the stretch ratio is usually from 1.1 to 8, preferably from 1.2 to 7,especially preferably from 1.5 to 6, in the longitudinal direction, andusually from 1.1 to 8, preferably from 1.2 to 7, especially preferablyfrom 1.5 to 6, in the transverse direction. The stretched product may beheat-set according to the purpose for which it is to be used.

As required, the stretched product of the copolyester of the inventionmay contain suitable amounts of various additives incorporated inconventional polyesters, for example, nucleating agents, inorganicfillers, lubricants, slip agents, antiblocking agents, stabilizers,antistatic agents, antihaze agents, and pigments. The stretched productof the copolyester of the invention may be produced by any of knownmethods. Generally, a starting molded article such as a film-likematerial, a sheet-like material or a parison molded from the copolyesteror its composition containing the above additives as required issubjected to a stretching treatment, either directly or after it iscooled to a temperature below its glass transition temperature andsolidified and then re-heated, at a temperature ranging from its glasstransition temperature to its melting point, preferably, from its glasstransition temperature to a point 80° C. higher than it. Theheat-setting of the stretched product is carried out for a short time atthe above stretching temperature or a higher temperature.

If the starting molded article is a film-like article or a sheet-likearticle, it may be stretched, for example, by a monoaxial stretchingmethod by which it is stretched in one direction, a biaxial stretchingmethod in which it is stretched in the longitudinal direction and thenin the transverse direction, a simultaneous biaxial stretching method inwhich it is stretched in the longitudinal and transverse directionssimultaneously, a method by which it is biaxially stretched and thenrepeatedly stretched in either one direction, a method by which it isbiaxially stretched and further in both directions, or a vacuum formingmethod by which a space between the film- or sheet-like article and themold is maintained in vacuum to thereby stretch it.

The stretched product of the copolyester may also be produced in theform of a laminate with another resin such as polyethyleneterephthalate. Such a laminate may be produced, for example, by a methodin which one or more layers of the starting molded article such as afilm- or sheet-like article of the copolyester are laminated to one ormore layers of a starting molded article such as a film- or sheet-likearticle of another resin such as polyethylene terephthalate, and thelaminate is then stretched, or a method in which a filmor sheet-likearticle of the other resin is bonded to the stretched product of thecopolyester of the invention.

If the starting molded article is a parison, a stretch blow-moldedcontainer may be produced from it by stretching the parison at the abovetemperature in the longitudinal direction, and then blow-molded tostretch it further in the transverse direction (biaxial stretch blowmolding). Furthermore, if a parison prepared from one or more layers ofthe copolyester and one or more layers of the other resin is subjectedto the above stretch blow molding, laminated blow-molded articlecomposed of the copolyester and the other resin (e.g., polyethyleneterephthalate) can be produced.

Since the stretched product of the copolyester of the invention hasexcellent gas-barrier property, it can be used in various applications.In particular, biaxially stretched blow-molded containers of thecopolyester, because of their excellent gas-barrier property, are usefulfor holding various articles, for example seasonings, oils, beer, winesand liquors, soft or carbonated drinks such as cola, cider and juices,cosmetics and detergent. Particularly, for holding beer or carbonateddrinks, the thickness of the containers can be decreased, and the tasteof these goods can be preserved for an extended period of time.

The stretched film of the copolyester of the invention may be used forexample, as electrically insulating film, magnetic tapes, photographicfilms, and metal-vapor deposited films.

The polyester composition of this invention comprises (A) 50% to 95% byweight of polyethylene terephthalate and (B) 50% to 5% by weight of acopolyester.

The polyester film, polyester preform and polyester container inaccordance with this invention are composed of the above polyestercomposition.

The polyester composition of this invention consists essentially of thepolyethylene terephthalate (A) and the copolyester (B). The dicarboxylicacid units of the copolyester (B) are composed of isophthalic acid unitsand 2,6-naphthalenedicarboxylic acid units and the dihydroxy compoundunits are composed of ethylene glycol units and1,3-bis(2-hydroxyethoxy)benzene units. Accordingly, the composition canbe dried at a high speed, and has excellent thermal resistance, impactstrength, transparency and gas-barrier property. Furthermore, since itdoes not contain high-melting oligomers, it has excellent surfaceproperties.

Now, the polyester composition, the polyester film, the polyesterpreform and the polyester container in accordance with this inventionwill be described in detail.

The polyethylene terephthalate (A) used in the polyester composition ofthe invention is a crystalline thermoplastic polyester composed ofusually at least 80 mole %, preferably at least 90 mole %, ofterephthalic acid units based on the entire dicarboxylic acid units andusually at least 80 mole %, preferably at least 90 mole %, of ethyleneglycol based on the entire dihydroxy compound units.

Examples of dicarboxylic acid units other than the terephthalic acidunits include units derived from aromatic dicarboxylic acids such asisophthalic acid, diphenylether-4,4-dicarboxylic acid,naphthalene-1,4dicarboxylic acid and naphthalene-2,6-dicarboxylic acid,aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipicacid, sebacic acid and undecanedicarboxylic acid, or aliphaticdicarboxylic acids such as hexahydroterephthalic acid.

Examples of dihydroxy compounds units other than the ethylene glycolunits are units derived from aliphatic dihydroxy compounds such aspropylene glycol, 1,4-butanediol and neopentyl glycol, aliphaticdihydroxy compounds such as propylene glycol, 1,4-butanediol andneopentyl glycol, alicyclic dihydroxy compounds such as cyclohexanedioland cyclohexanedimethanol, and aromatic dihydroxy compounds such as1,3-bis(2-hydroxyethoxy)benzene, 1,4-bis(2-hydroxyethoxy)benzene,2,2-bis(4-beta-hydroxyethoxyphenyl)propane,bis(4-beta-hydroxyethoxyphenyl)sulfone and bisphenol A.

The polyethylene terephthalate (A) may contain the other dicarboxylicacid units and the other dihydroxy compound units if it containsterephthalic acid units and ethylene glycol units in the amountsindicated above. The polyethylene terephthalate (A) may be used as amixture with another polyester.

The molecular weight of the polyethylene terephthalate (A) is notparticularly limited if it is within a range which can give variousmolded articles such as a container from the resulting polyestercomposition. However, polyethylene terephthalate (A) used in thisinvention desirably has an intrinsic viscosity [η], measured ino-chlorophenol at 25° C., of at least 0.6 dl/g, preferably at least 0.8dl/g.

The copolyester (B) contained in the polyester composition is composedof the dicarboxylic acid units and the dihydroxy compound units to bedescribed below, and can be obtained by the copolycondensation of thecorresponding dicarboxylic acids and dihydroxy compounds.

If the amount of the isophthalic acid units exceeds 95 mole %, the glasstransition temperature of the copolyester (B) does not so much increase.If, on the other hand, it is less than 60 mole %, the glass transitiontemperature of the copolyester (B) rises too much, and a blend of thecopolyester (B) and polyethylene terephthalate (A) cannot sufficientlybe stretched.

Since the copolyester (B) contains 2,6-naphthalenedicarboxylic acidunits derived from a rigid comonomer, the copolyester has a high glasstransition temperature and a high level of gas-barrier property.Accordingly, the polyester composition composed of the copolyester (B)and polyethylene terephthalate (A) can be dried at a high speed duringproduction.

Various known methods may be used to prepare the polyester compositionfrom the polyethylene terephthalate (A) and the copolyester (B). Forexample, there may be used a method by which the polyethyleneterephthalate (A) and the copolyester (B) are mixed by using a Henschelmixer, a V-blender, a ribbon blender, a tumbler blender, etc. Since thecopolyester has a high glass transition temperature, even when the twopolyesters (A) and (B) are mixed immediately after drying, thecopolyester hardly melt-adheres to itself. Accordingly, the twopolyesters (A) and (B) can be rapidly mixed after drying. The mixture soprepared may be melt-kneaded by a single-screw extruder, a twin-screwextruder, a kneader or a Bambury mixer, and then granulated orpulverized.

In the resulting polyester composition, the amount of the polyethyleneterephthalate (A) is 50% to 95% by weight, preferably 70% to 90% byweight, and the amount of the copolyester (B) is 50% to 5% by weight,preferably 30% to 10% by weight, based on the total weight of thepolyester composition.

If the amount of the polyethylene terephthalate (A) is less than 50% byweight, the properties of the polyethylene terephthalate cannotsufficiently be exhibited. On the other hand, if it exceeds 95% byweight, the properties of the copolyester (B) are not fully exhibited.

The resulting polyester composition has a glass transition temperatureof usually 75° C. to 85° C., preferably 80° C. to 85° C. Since thepolyester composition of the invention has a higher glass transitiontemperature than a polyester composition comprising a conventionalisophthalate-type copolyester, it can be dried at high temperatures, andtherefore rapidly.

The polyester composition of this invention may contain ordinary variousadditives for polyesters, such as heat stabilizers, weather stabilizers,antistatic agents, lubricants, mold releasing agents, pigment dispersingagents, pigments and dyes in amounts which do not impair the objects ofthis invention.

The polyester composition may be used in various shapes such as a sheet,a plate, a tube, a hollow article or a container.

The polyester film in accordance with this invention is prepared by anordinary method from the polyester composition described above. Thepolyester film may either be stretched or unstretched.

The unstretched polyester film desirably has a thickness of usually 50to 900 micrometers, preferably 200 to 600 micrometers.

The stretched film may be a monoaxially or biaxially stretched film. Thestretch ratio of the monoaxially stretched film is desirably from 1.1 to10, preferably from 1.2 to 8, especially preferably from 1.5 to 7. Inthe biaxially stretched film, the stretch ratio is usually from 1.1 to8, preferably from 1.2 to 7, especially from 1.5 to 7.

In the biaxially stretched film, the stretch ratio is desirably from 1.1to 8, preferably from 1.2 to 7, especially preferably from 1.5 to 6, inthe longitudinal direction, and from 1.1 to 8, preferably from 1.2 to 7,especially preferably from 1.5 to 6, in the transverse direction.

The polyester film of this invention can be produced by any knownmethod. Generally, a film-like material molded from the above polyestercomposition optionally containing the additives, as such or after it iscooled and solidified at a temperature below the glass transitiontemperature, is re-heated, and this starting molded product is subjectedto a stretching treatment at a temperature ranging from the glasstransition temperature to its melting point, preferably from the glasstransition temperature to a point about 80° C. higher than the glasstransition temperature. Heat-setting of the stretched film may becarried out at a temperature higher than the above stretchingtemperature for a short period.

In the production of the stretched polyester film of this invention, thestarting film-like product in the unstretched state may be stretchedmonoaxially (monoaxial stretching method); stretched in the longitudinaldirection and then in the transverse direction (biaxial stretchingmethod); stretched simultaneously in the longitudinal and the transversedirections (simultaneous biaxial stretching method); stretched biaxiallyand then repeatedly stretching in either direction; stretched biaxiallyand further in both directions; or may be processed by a so-calledvacuum forming method in which a space between the film-like product anda mold is reduced in pressure, thereby to stretch-mold the film-likeproduct.

The polyester composition of this invention may be processed into asheet-like article substantially in accordance with the methods ofproducing the polyester film described above.

The polyester preform of this invention may be produced by using thepolyester composition.

For example, it may be prepared by injection molding the polyestercomposition.

The polyester container in accordance with this invention may beproduced by press-forming a sheet of the polyester composition, orstretch blow-molding the polyester preform mentioned above.

Stretch blow-molding may be carried out, for example, by stretching thepreform in the longitudinal direction at the stretching temperature forthe polyester composition, and then blow-molding it to stretch it alsoin the transverse direction (biaxial stretch blow molding method).

To produce the polyester container from the biaxial stretch blow moldingmethod, a bottomed preform molded by an ordinary injection-moldingmachine or a parison obtained by bottoming one end of a parison moldedby an extrusion-molding machine is stretched to 1.5 to 3.5 times,preferably 2 to 3 times in the longitudinal direction, and 2 to 5 times,preferably 3 to 4.5 times, in the transverse direction at a stretchingtemperature of 80° C. to 120° C., preferably 90° C. to 110° C. by a rodmoving longitudinally within a blow molding mold and the blowing of apressurized gas. Molding by an injection molding machine may be carriedout by a two-stage method using a cold parison or a one-stage methodusing a hot parison.

To improve the rigidity of the polyester container, a layer ofpolyethylene terephthalate may be laminated to the inside and outsidelayers of the polyester composition.

The polyester container of this invention may be used in variousapplications because of its excellent transparency and gas-barrierproperty In particular, biaxial stretch blow-molded containers haveexcellent gas-barrier property and transparency and can be used not onlyfor holding seasonings, oils, wines and liquors, cosmetics anddetergents, but also holding sparkling drinks such as cola, cider andbeer. The polyester containers of the invention permit prolongation ofthe period within which goods held therein can be taken with theiroriginal tastes and flavors without increasing the thickness of thecontainer wall as in conventional containers.

The polyester laminated structure of this invention is composed of (C) apolyalkylene terephthalate layer and (B) a copolyester layer. Thecopolyester layer (D) is a layer of the copolyester of the inventiondescribed hereinabove, or the above polyester composition of theinvention comprising the copolyester and polyethylene terephthalate, inwhich the layers (C) and (D) are stretched.

The preform for the polyester laminated blow-molded product of thisinvention is composed of (C) a polyalkylene terephthalate and (D) acopolyester layer which is a layer of the copolyester of the inventiondescribed hereinabove, or the above polyester composition of theinvention comprising the copolyester and polyethylene terephthalate.

The polyester laminated blow-molded product of this invention iscomposed of (A) a polyalkylene terephthalate and (D) a copolyesterlayer. The copolyester layer is a layer of the copolyester of theinvention described above and the polyester composition of the inventioncomprising the copolyester and polyethylene terephthalate.

The polyester laminated structure, the preform for a laminatedblow-molded article, and the laminated blow-molded article in accordancewith this invention are each composed of the above described specificlayers mentioned above, and therefore, have excellent gas-barrierproperty particularly with respect to oxygen and carbon dioxide, thermalresistance, impact strength, surface properties, transparency,electrical properties and chemical resistance and hardly containhigh-melting oligomers.

The polyester laminated structure, the preform for a laminatedblow-molded article, and the laminated blow-molded article in accordancewith this invention will be described below specifically.

The polyalkylene terephthalate layer (C) of the polyester laminatedstructure of the invention is formed of a polyalkylene terephthalatesuch as polyethylene terephthalate and polypropylene terephthalate,preferably polyethylene terephthlate.

The polyethylene terephthalate used in this invention is as describedhereinabove.

The molecular weight of polyethylene terephthlate used in this inventionis not particularly limited if the resulting polyester laminatedstructure can be molded into various articles such as a container.Desirably, however, the polyethylene terephthalate has an intrinsicviscosity [η], measured at 25° C. in o-chlorophenol, of usually at least0.6 dl/g, preferably at least 0.8 dl/g.

When polypropylene terephthalate, for example, is used as thepolyalkylene terephthalate, propylene glycol may be used in place ofethylene glycol. The polypropylene terephthalate so obtained has anintrinsic viscosity, measured at 25° C. in o-chlorophenol, of usually0.8 to 1.2 dl/g. This polypropylene terephthalate may be used as amixture with another polyester.

The copolyester layer (D) of the polyester laminated structure in thisinvention may be formed from the above copolyester or a polyestercomposition comprising the copolyester and polyethylene terephthalatedescribed hereinabove. If the proportion of isophthalic acid unitsconstituting the above copolyester exceeds 95 mole %, the glasstransition temperature of the copolyester do not so much increase. If itis less than 60 mole %, the glass transition temperature of thecopolyester increases excessively, and the polyester laminated structurecomposed of the copolyester layer (D) and the polyalkylene terephthalatelayer (C) can be stretched only with reduced stretchability of thecopolyester layer (D).

In the present invention 2,6-naphthalenedicarboxylic acid units derivedfrom a rigid comonomer component are included as units constituting thecopolyester. Hence, the copolyester has a high glass transitiontemperature and hardly contain high-melting oligomers. The gas-barrierproperty of the laminated structure can be maintained at a high level.

The polyester composition used in the production of the polyesterlaminated structure has a higher glass transition temperature than apolyester composition comprising a conventional isophthalate-typecopolyester, and therefore can be dried rapidly at a high temperature,and the polyester laminated structure of the invention can be producedefficiently.

Specific examples of the laminated structure are shown below.

A two-layer laminated structure composed of one copolyester layer (D)and one polyalkylene terephthalate layer (C);

a three-layer laminated structure composed of two outside layers of thepolyalkylene terephthalate (C) and an interlayer of the copolyester (D);

a multilayer laminated structure having four or more layers composed ofalternately laminated layers of the copolyester (D) and layers ofalkylene terephthalate (C), in which both outermost layers are composedof the polyalkylene terephthalate (C);

a multilayer laminated structure having four or more layers composed ofalternately laminated layers of the copolyester (D) and layers ofalkylene terephthalate (C), in which both outermost layers are composedof the copolyester (D); and

a multilayer laminated structure having four or more layers composed ofalternately laminated layers of the copolyester (D) and layers ofalkylene terephthalate (C), in which one of the outermost layers iscomposed of the copolyester layer (D) and the other, of the polyalkyleneterephthalate layer (C).

The laminated structures may be used in the form of a sheet, a plate, atube, a hollow body or a container, and can be produced by knownmethods.

There is no particular restriction on the thicknesses of the copolyesterlayer (D) and the polyalkylene terephthalate layer (C) and may bedetermined according to the use to which the resulting laminatestructure is to be put. For example, when this laminated structure is atwo-layer structure, the thickness of the copolyester layer (D) isusually 50 to 500 micrometers, preferably 50 to 300 micrometers, and thethickness of the polyalkylene terephthalate layer (C) is 50 to 300micrometers, preferably 50 to 200 micrometers. When the laminatedstructure is the first-mentioned three layer structure, the thickness ofthe copolyester layer (D) is usually 50 to 500 micrometers, preferably50 to 200 micrometers. The thickness of each of the outside polyalkyleneterephthalate layer (C) is usually 50 to 500 micrometers, preferably 50to 300 micrometers. If the laminated structure is the latter-mentionedthree-layer structure, the thickness of the polyalkylene terephthalateinterlayer is usually 50 to 500 micrometers, preferably 50 to 300micrometers, and the thickness of copolyester outside layers (C) isusually 50 to 500 micrometers, preferably 50 to 200 micrometers. Whenthe laminated structure is a multilayer structure, the thicknesses ofthe intermediate layer and both outside layers of the copolyester (D)and the thicknesses of the intermediate layer and outermost layerscomposed of the polyalkylene terephthalate layer (C) may be prescribedin the same way as above.

The laminated structure of the invention has excellent stretchability,electrical properties, particularly electrical insulation, mechanicalstrength, transparency and gas-barrier property.

The polyester stretched laminated structure of the invention may beproduced by any known methods. Generally, a starting molded article suchas a film or sheet obtained by laminating the polyalkylene terephthalatelayer (C) and the copolyester layer (D), either as such or after coolingand solidifying it to a temperature below the glass transitiontemperature of the polyalkylene terephthalate and the copolyester, isstretched at a temperature above the glass transition temperature ofboth, preferably 70° C. to 100° C.

The polyester stretched laminated molded structure of the invention canbe produced by, for example monoaxially, stretching an unstretched filmor sheet (when the starting molded article is film or sheet) (monoaxialstretching method); stretched in the longitudinal direction and then inthe transverse direction (biaxial stretching method); stretchedbiaxially and then repeatedly stretched in either direction; orbiaxially stretched and then further stretched in both directions. Whenthe starting structure is to be monoaxially stretched, the stretch ratiois usually from 1.1 to 10, preferably from 1.2 to 8, especiallypreferably from 1.5 to 7. In the production of the starting moldedstructure by biaxial stretching, the stretch ratio is usually from 1.1to 8, preferably from 1.2 to 7, especially preferably from 1.5 to 6, inthe longitudinal direction, and usually from 1.1 to 8, preferably from1.2 to 7, especially preferably from 1.5 to 6, in the transversedirection. The resulting stretched laminated molded structure may beheat-set.

The polyester stretched laminated structure of the invention hasexcellent mechanical strength, transparency, electrical properties andgas-barrier property. In particular, by using this molded structure forforming electrical and electronic component parts and metallic parts, itis effective for protecting electrical and electronic circuits andpreventing corrosion of metals. The polyester stretched laminatedstructure in the form of a film can also be effectively used forcapacitors, motors, transformers and wire and cable coatings byutilizing its electrical properties. Furthermore, by utilizing itsexcellent gas-barrier property, it may be used as a film for foodpackaging.

The preform for the polyester laminated blow-molded article of theinvention may be produced by using the polyester laminated structure ofthe invention.

For example, by molding and processing the polyester laminated structurein tubular form, the preform of the invention can be obtained.

The polyester laminated blow-molded article of this invention is astretch blow-molded article formed from the above polyester laminatedstructure. The stretched blow-molded article may be produced by stretchblow-molding the above preform.

The polyester laminated blow-molded article may be monoaxially orbiaxially stretched. The biaxially stretched polyester laminatedblow-molded article has outstanding mechanical strength and gas-barrierproperty.

The stretch ratios used in the production of the polyester laminatedblow-molded article in this invention may be the same as those describedabove with regard to the stretched polyester laminated structures.

The polyester laminated blow-molded article may be produced bystretching and blow-molding the preform described above. The stretchblow molding may be carried out by stretching the preform in thelongitudinal direction at temperatures within the range of thestretching temperatures for the laminated structure, and furtherblow-molding the stretched preform to stretch it in the transversedirection (biaxial stretching blow-molding method).

For example, a polyester container may be produced in accordance withthe biaxial stretching blow-molding method by stretching a bottomedparison molded by an ordinary injection-molding machine, or a parisonobtained by bottoming one end of a parison molded by an extrusionmolding machine at a temperature of 80° C. to 120° C., preferably 90° C.to 110° C., to 1.5 to 3.5 times in the longitudinal direction, and to 2to 5 times, preferably 3 to 4.5 times in the transverse direction by arod moving longitudinally within a blow-molding mold and the blowing ofa pressurized gas. Particularly, a biaxially stretched blow-moldedcontainer as the polyester laminated blow-molded article of theinvention has excellent gas-barrier property and transparency, and issuitable therefor for holding not only seasonings, oils, wines andliquors, cosmetics and detergents but also for holding sparkling drinkssuch as cola, cider and beer as stated hereinabove.

The following examples illustrate the present invention specifically.

In these examples, the various properties were measured by the followingmethods.

Intrinsic viscosity of the polyester

Measured in an o-chlorophenol solution of the polymer at 25° C.

Composition of the polyester

Determined by measuring the nuclear magnetic resonance spectrum of thepolyester in a trichloroacetic acid solution.

Glass transition temperature of the polyester

Measured by a differential scanning calorimeter at a temperatureelevating rate of 10° C./min.

Oxygen gas permeation coefficient

Measured at 25° C. by an OXTRAN device made by MOCON company.

Carbon dioxide gas permeability coefficient

Measured at 25° C. by using a PERMATRAN C-IV device made by MOCONcompany.

EXAMPLE A1

A copolyester composed of isophthalic acid (IA),2,6-naphthalenedicarboxylic acid (NDA), 1,3-bis(2-hydroxyethoxy)benzene(DER) and ethylene glycol (EG) was produced by the following procedure.

A 1-liter stainless steel reactor equipped with a stirrer, a nitrogengas inlet and a condenser was charged with 122.5 g of isophthalic acid,17.7 g of naphthalenedicarboxylic acid, 94.8 g of ethylene glycol, 24.4g of 1,3-bis(2-hydroxyethoxy)benzene, 0.33 g of1,1,1-trishydroxymethylpropane, 0.058 g of titanyl acetylactonate, 0.077g of Sb₂ O₃, 0.010 g of tetrasodium ethylenediaminetetraacetate, and0.027 g of manganese hypophosphate monohydrate.

The reaction mixture was heated in an atmosphere of nitrogen at 220° C.for 1 hour and then at 240° C. for 25 minutes. During this time, waterwas continuously evaporated.

Then, 0.164 g of tris(nonylphenyl) phosphite was added to the mixture inthe reactor.

The reaction temperature was raised to 250° C., and maintained for 35minutes in a nitrogen atmosphere.

The flowing of the nitrogen gas was stopped, and a reduced pressure ofless than 4 mmHg was applied. The reaction was continued at 275° C. for4 hours under less than 0.4 mmHg. The resulting copolyester had anintrinsic viscosity of 0.83 dl/g. It had a glass transition temperatureof as high as 70° C. The carbon dioxide gas permeability coefficient was3.0 cc.mm/m² day.atm, and it had good gas-barrier property.

EXAMPLES A2 and A3 and COMPARATIVE EXAMPLES A-1 to A-6

Copolyesters having the compositions indicated in Table 1 weresynthesized as in Example A1. Sheets were formed from the copolyesters,and their gas-barrier properties were measured.

The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                               Composition of         Pco.sub.2                                              the copolyester Tg     (cc · mm/m.sup.2                                                              [η]ot.                             Run (*)                                                                              (mole %)        (°C.)                                                                         day · atm)                                                                    (dl/g)                                 ______________________________________                                        Ex. Al IA/NDA/DER/EG   73     3.0      0.83                                          90/10/15/85                                                            Ex. A2 IA/NDA/DER/EG   78     3.1      0.81                                          80/20/15/85                                                            Ex. A3 IA/NDA/DER/EG   84     3.3      0.83                                          70/30/15/85                                                            CEx. A1                                                                              TA/EG           78     21.8     0.75                                          100/100                                                                CEx. A2                                                                              IA/EG           67     3.0      0.80                                          100/100                                                                CEx. A3                                                                              NDA/EG          124    7.2      0.80                                          100/100                                                                CEx. A4                                                                              IA/NDA/DER/EG   90     4.2      0.80                                          50/50/15/85                                                            CEx. A5                                                                              IA/TA/EG/DER    69     3.8      0.78                                          70/30/85/15                                                            CEx. A6                                                                              IA/TA/EG/DER/BSE                                                                              78     5.1      0.81                                          70/30/72/15/12                                                         ______________________________________                                         Ex. = Example;                                                                CEx. = Comparative Example                                               

The total amount of the dicarboxylic acid and the dihydroxy compound was100 mole %.

The following abbreviations were used.

IA: isophthalic acid

NDA: 2,6-naphthalenedicarboxylic acid

TA: terephthalic acid

DER: 1,3-bis(2-hydroxyethoxy)benzene

EG: ethylene glycol

BSE bis(4-beta-hydroxyethoxyphenyl)sulfone

EXAMPLES B1 to B6 and COMPARATIVE EXAMPLES B1 to B8

One hundred parts of polyethylene terephthalate (Mitsui PET J135, aproduct of Mitsui PET Resin Co., Ltd.) dried at 150° C. for 10 hours wasmixed with each of the amounts indicated in Table 2 of the copolyesterobtained in Example A1. The mixture was melt-extruded at a moldingtemperature of about 250° C. to 290° C. by an extruder, cooled and cutby a cutter to form pellets of a polyester composition composed ofpolyethylene terephthalate and the copolyester. The pellets werepress-formed to prepare a press sheet having a thickness of about 600micrometers. The press sheet was stretched simultaneously by a biaxiallystretching device to three times both in the longitudinal and transversedirections to obtain a biaxially stretched film.

The resulting biaxially stretched film has a thickness of about 50microns, there was no thickness unevenness, and it was uniformlystretched. The transparencies and the carbon dioxide gas permeabilitycoefficients of the press sheet and the biaxially stretched film areshown in Table 2.

The compositions obtained by mixing PET with the copolyesters ofComparative Examples A2 and A5 had a decreased glass transitiontemperature as compared with the compositions prepared by mixing PETwith the copolyesters of Examples A1, A2 and A3. Furthermore, when thecopolyesters of Comparative Examples A5 and A6 were mixed with PET, theeffect of improving the oxygen gas permeability coefficient was small

                  TABLE 2                                                         ______________________________________                                                           Properties of the                                                             biaxially stretched film                                                      of the composition                                         Copolyester      Tg of          CO.sub.2 gas                                         Type              the        permeability                                     (example          compo-     coefficient                                      designa- Amount   sition                                                                              Haze (cc · mm/m.sup.2 ·      Run    tion)    (wt. %)  (°C.)                                                                        (%)  day · atm)                       ______________________________________                                        Ex. B1 Ex. A1   10       77    0.6  9.1                                       Ex. B2 Ex. A2   10       78    0.6  9.3                                       Ex. B3 Ex. A3   10       79    0.6  9.5                                       CEx. B1                                                                              CEx. A2  10       73    2.0  9.1                                       CEx. B2                                                                              CEx. A4  10       79    1.0  10.1                                      CEx. B3                                                                              CEx. A5  10       73    0.7  9.9                                       CEx. B4                                                                              CEx. A6  10       78    1.2  10.6                                      Ex. B4 Ex. A1   20       77    0.8  7.5                                       Ex. B5 Ex. A2   20       78    0.8  7.6                                       Ex. B6 Ex. A3   20       79    0.9  7.9                                       CEx. B5                                                                              CEx. A2  20       70    2.8  7.5                                       CEx. B6                                                                              CEx. A4  20       80    1.2  8.7                                       CEx. B7                                                                              CEx. A5  20       70    0.8  8.7                                       CEx. B8                                                                              CEx. A6  20       78    1.4  9.4                                       ______________________________________                                    

EXAMPLES B7 to B9 and COMPARATIVE EXAMPLES B9 to B11

The composition of polyethylene terephthalate and the copolyestersprepared in Examples B1, B3 and B5 were each injection-molded at amolding temperature of about 270° C. by an injection-molding machine toform preforms (cold parison). Each of the preforms was biaxiallystretched and blow-molded to about 2.5 times in the longitudinaldirection and about 4 times in the transverse direction to produce astretched bottle having an inner capacity of about 1 liter.

The above procedure was repeated using the polyester compositions ofComparative Examples B3, B5 and B7.

The hazes of the side surfaces of the stretched bottles and their carbondioxide gas permeabilities were measured, and the results are shown inTable 3.

                  TABLE 3                                                         ______________________________________                                                    Properties of the biaxially                                                   stretched bottle                                                         Composition                                                                              Haze (%) of CO.sub.2 gas permeation                                (example   the side surface                                                                          coefficient                                     Run    designation)                                                                             of the bottle                                                                             (cc/day · bottle ·            ______________________________________                                                                      atm)                                            Ex. B7 Ex. B1     1.8         1.5                                             Ex. B8 Ex. B3     2.0         1.5                                             Ex. B9 Ex. B5     2.4         1.6                                             CEx. B9                                                                              CEx. B3    2.8         2.1                                             CEx. B10                                                                             CEx. B5    2.0         1.9                                             CEx. B11                                                                             CEx. B7    3.0         2.8                                             ______________________________________                                    

EXAMPLE C1

Polyethylene terephthalate (Mitsui PET J135, a product of Mitsui PETResin Co., Ltd.) dried at 150° C. for 10 hours was press-formed at about260° C. to prepare a press sheet having a thickness of about 100micrometers.

Separately 100 parts of the polyethylene terephthalate was mixed with 20parts of the copolyester of Example A1, and the mixture wasmelt-extruded at 260° C. to 280° C. by using an extruder to producepellets of the composition. The pellets of the composition werepress-formed at about 260° C. to prepare a press sheet having athickness of about 100 micrometers. The above polyethylene terephthalatepress sheet was laid over the press sheet of the composition, and theassembly was press-formed at about 260° C. to give a two-layer laminatedsheet having a thickness of about 600 micrometers. The resultinglaminated sheet had good adhesion between the polyethylene terephthalatelayer (C) and the polyester composition layer (D) and had a haze of1.2%. The carbon dioxide gas permeability coefficient was 15.5cc.mm/m².day.atm.

The laminated sheet was simultaneously stretched in the longitudinal andtransverse direction to 3 times by a biaxially stretching device toprepare a biaxially stretched film having a thickness of about 50micrometers. The film was in the uniformly stretched state. Thebiaxially stretched film also shows good adhesion between thepolyethylene terephthalate layer (C) and the polyester composition layer(D). The film had a haze of 0.6%, and a carbon dioxide gas permeabilitycoefficient of 10.0 cc.mm/m².day.atm.

EXAMPLES C2 and C3 and COMPARATIVE EXAMPLES C1 to C4

In the same way as in Example C1, press sheets and biaxially stretchedfilms were prepared except that the copolyesters indicated in Table 4were used. The haze values and carbon dioxide gas permeabilitycoefficients of the products are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                                  Properties of the biaxially                     Copolyester    Properties of the press sheet                                                                stretched film of the                           Type           of the laminated structure                                                                   laminated structure                                  (example                                                                           Amount  CO.sub.2 gas permeability                                                                    CO.sub.2 gas permeability                         design-                                                                            (parts by                                                                          Haze                                                                             coefficient Haze                                                                             coefficient                                  Run  ation)                                                                             weight)                                                                            (%)                                                                              (cc · mm/m.sup.2 · day ·                           atm)        (%)                                                                              (cc · mm/m.sup.2 · day                                      · atm)                              __________________________________________________________________________    Ex. Cl                                                                             Ex. A1                                                                             20   1.2                                                                              15.5        0.6                                                                              10.0                                         Ex. C2                                                                             Ex. A2                                                                             20   1.6                                                                              15.7        0.8                                                                              10.1                                         Ex. C3                                                                             Ex. A3                                                                             20   1.8                                                                              16.0        0.9                                                                              10.2                                         CEx. C1                                                                            CEx. A2                                                                            20   5.2                                                                              15.5        2.1                                                                              10.0                                         CEx. C2                                                                            CEx. A4                                                                            20   2.4                                                                              17.2        1.2                                                                              10.6                                         CEx. C3                                                                            CEx. A5                                                                            20   1.6                                                                              17.0        0.8                                                                              11.0                                         CEx. C4                                                                            CEx. A6                                                                            20   2.8                                                                              19.0        1.4                                                                              11.0                                         __________________________________________________________________________

EXAMPLE C4

The polyethylene terephthalate in Example C1 was injection-molded, andthen a composition composed of 100 parts of the polyethyleneterephthalate in Example C1 and 20 parts of the copolyester in ExampleA1 was also injection-molded to form a preform having an inside layer ofthe polyethylene terephthalate (C) and an outside layer of the polyestercomposition (D) composed of the copolyester and the polyethyleneterephthalate each of the layers having a thickness of about 1.6 mm.

The resulting preform was heated to 85 to 95° C. by using a far-infraredheater, and then stretched to about 2.5 times in the longitudinaldirection and to about 4.3 times in the transverse direction bystretching blow-molding machine to prepare a two-layer stretched bottlehaving an inner capacity of about 1 liter in which the polyethyleneterephthalate layer (C) in the minimum thickness portion was about 150micrometers thick, and the polyester composition layer (D) was about 150micrometers thick. The haze of the side surface of the stretched bottlewas 1.5%. The carbon dioxide gas permeability of this bottle was 2.0ml/day bottle.atm.

COMPARATIVE EXAMPLE C5

A preform composed only of polyethylene terephthalate and having thesame thickness (about 3.2 mm) of the preform in Example C5 was preparedby injection molding the polyethylene terephthalate used in Example 1.The preform was then stretched and blow-molded to prepare a stretchedbottle having an inner capacity of about 1 liter in which the minimumthickness portion was about 300 micrometers thick.

The side surface of the stretched bottle had a haze of 4.5%, and thecarbon dioxide gas permeability of the stretched bottle was 2.0 ml/daybottle.atm.

We claim:
 1. A copolyester having an intrinsic viscosity, measured ino-chlorophenol at 25° C., of 0.3 to 1.5 dl/g and being derived fromdicarboxylic acid units composed of 95 to 60 mole % of isophthalic acidunits and 5 to 40 mole % of 2,6-naphthalenedicarboxylic acid units anddihydroxy compound units composed of 95 to 70 mole % of ethylene glycolunits and 5 to 30 mole % of 1,3-bis(2hydroxyethoxy)benzene units.
 2. Acopolyester according to claim 1 having an intrinsic viscosity, measuredin o-chlorophenol at 25° C., of 0.6 to 1.0 dl/g and being derived fromdicarboxylic acid units composed of 90 to 70 mole % of isophthalic acidunits and 10 to 30 mole % of 2,6-naphthalenedicarboxylic acid units anddihydroxy compound units composed of 90 to 80 mole % of ethylene glycolunits and 10 to 20 mole % of 1,3-bis(2-hydroxyethoxy)benzene units. 3.The copolyester of claim 2 which further comprises 0.01 to 2 mole, per100 mole of the dihydroxy compound units, of trifunctional orhigher-functional polyhydroxy compound units.
 4. The copolyester ofclaim 2 which further comprises 0.05 to 1 mole, per 100 moles of thedihydroxy compound units, of 1,1,1-tris(hydroxymethyl)propane units. 5.A gas-barrier property imparting agent comprising a copolyester havingan intrinsic viscosity, measured in o-chlorophenol at 25° C., of 0.3 to1.5 dl/g and being derived from dicarboxylic acid units composed of 95to 60 mole % of isophthalic acid units and 5 to 40 mole % of2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 95 to 70 mole % of ethylene glycol units and 5 to 30 mole %of 1,3-bis(2hydroxyethoxy)benzene units.
 6. A gas-barrier propertyimparting agent according to claim 5 comprising a copolyester having anintrinsic viscosity, measured in o-chlorophenol at 25° C., of 0.6 to 1.0dl/g and being derived from dicarboxylic acid units composed of 90 to 70mole % of isophthalic acid units and 10 to 30 mole % of2,6-naphthalenedicarboxylic acid units and dihydroxy compound unitscomposed of 90 to 80 mole % of ethylene glycol units and 10 to 20 mole %of 1,3-bis(2-hydroxyethoxy)benzene units.
 7. The gas-barrier propertyimparting agent of claim 6 in which the copolyester further comprises0.01 to 2 moles, per 100 moles of the dihydroxy compound units, oftrifunctional or higher-functional polyhydroxy compound units.
 8. Thegas-barrier property imparting agent of claim 6 in which the copolyesterfurther comprises 0.05 to 1 mole, per 100 moles of the dihydroxycompound units, of 1,1,1-tris(hydroxymethyl)propane units.